Abstract: A fluid exchanger for servicing the fluid circuits of vehicular power steering systems and other fluid circulating or hydraulic circuits. The fluid exchanger uses a float operated fluid control valve to harness fluid pressure provided by a pump of an accessed hydraulic circuit. The fluid control valve uses both negative and positive pressure of the circuit's pump to control fluid flow patterns. The float and fluid control valve are matched to be either mechanical/hydraulic or electrical/hydraulic in design. If the exchanger is provided with a mechanically operated fluid control valve, a mechanical float is provided in the exchanger's fresh fluid reservoir and is directly connected to the valve slide of the fluid control valve. If the exchanger is provided with an electric solenoid operated fluid control valve, a float operated electrical switch is provided in the exchanger's fresh fluid reservoir and is wired to control the solenoid of the valve.